The performance of a fiber optic system is assessed through various parameters, such as insertion loss (IL), polarisation dependent loss (PDL) and polarization mode dispersion (PMD). Among the few methods known to calculate the PDL, the method of using the Mueller matrix makes possible accurate and rapid measurements. It consists in launching four different orthogonal states of polarization to a DUT. The measurement of the optical power transmitted in these four polarization states enables the calculation of the PDL of the component. One application of the method is disclosed in U.S. Pat. No. 5,371,597.
As is known, for determining the PDL and the IL, a polarization controller is needed to generate four orthogonal states of polarization. The polarization controller typically comprises a polarizer and fractional-wave plates, also referred to as retardation plates or birefringent plates or phase shifters. The polarizer insures a constant linear input polarization. The fractional-wave plates are orientated so as to obtain desired polarization states.
Knowing the input signal by its Stokes vector Sij in each state of polarization, the Stokes vector Sij out of the output signal is obtained by multiplication using the Mueller matrix mij. To determine the PDL and IL, the only terms that one needs to obtain are those of the top row of the Mueller matrix (mij).